The purpose of this project is to synthesize a variety of organic compounds labelled with gamma-emitting nuclides and to ascertain their ability to selectively concentrate in tumors or organs. The rationale for the design of these compounds is generally based on published biochemical and/or pharmacological findings. Agents for the clinical diagnosis of uveal melanoma and adrenal cortical tumors have resulted from this project. Current research emphasizes the synthesis of agents with the potential of visualizing prostate, pancreas, adrenal medulla and associated tumors. A variety of radiolabelled estrogens are being examined for their ability to selectively concentrate in mammary tumors. While current research is focused on the development of diagnostic imaging agents for a variety of endocrine tumors, agents which display a potential for photoscanning other organs will not be ignored. BIBLIOGRAPHIC REFERENCES: Counsell, R. E., Ranade, V. V., Kline, W., Hong, B. H. and Buswink, A. A.: Potential Organ or Tumor Imaging Agents, XV. Radioiodinated Phenytoin Derivatives. J. Pharm. Sci. 65: 285 (1976). Korn, N., Buswink, A., Yu, T., Carr, E. A., Carroll, M. and Counsell, R. E.: A Radioiodinated Bretylium Analog as a Potential Agent for Scanning Adrenal Medulla. J. Nuc. Med. 18: 87 (1977).